package List;

/**
 * 给你一个链表，删除链表的倒数第 n 个结点，并且返回链表的头结点。
 * 示例 1：
 * 输入：head = [1,2,3,4,5], n = 2
 * 输出：[1,2,3,5]
 * 示例 2：
 * 输入：head = [1], n = 1
 * 输出：[]
 * 示例 3：
 * 输入：head = [1,2], n = 1
 * 输出：[1]
 */
public class RemoveNthFromEnd19 {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        if (head == null) {
            return null;
        }
        ListNode dummyNode = new ListNode(-1);
        dummyNode.next = head;
        ListNode slow = dummyNode;
        ListNode fast = dummyNode;
        while (n >= 0) {
            fast = fast.next;
        }
        while(fast != null){
            slow = slow.next;
            fast = fast.next;
        }
        slow.next = slow.next.next;

        return dummyNode.next;
    }

}
